Influence of Sweetpotato Resistance on the Development of Meloidogyne enterolobii and M. incognita.

Meloidogyne enterolobii and M. incognita are major pests of sweetpotato. The ability of M. enterolobii to cause symptoms and reproduce on nematode-resistant cultivars threatens the sweetpotato industry. To evaluate the penetration, development, and reproduction of M. enterolobii and M. incognita on sweetpotato, a time-course study was conducted using the genotypes 'LA14-31' (resistant to M. enterolobii and intermediate-resistant to M. incognita), 'LA18-100' (susceptible to M. enterolobii and resistant to M. incognita), and 'LA19-65' (resistant to M. enterolobii and susceptible to M. incognita), with 'Beauregard' (susceptible to both species) and 'Jewel' (resistant to M. enterolobii and intermediate-resistant to M. incognita) as controls. Sweetpotato roots were collected at 7-, 9-, 11-, 13-, 21-, and 35-days post-inoculation (DPI), stained with acid fuchsin, and analyzed for nematode developmental stages. Nematode reproduction was evaluated by examining egg production at 42 DPI. Results showed that M. enterolobii developed and reproduced only in 'Beauregard' and 'LA18-100'. In resistant genotypes such as 'Jewel', 'LA14-31', and 'LA19-65', M. enterolobii remained at the pre-parasitic J2-stage, with halted development linked to localized cell death in response to M. enterolobii penetration. For M. incognita, the defense response was most notable in 'LA18-100', where infective juveniles either died, matured as males, or experienced delayed development into adult females, with a marked reduction in M. incognita reproduction. These findings suggest that resistance to M. enterolobii likely involves a hypersensitive-like response that prevents feeding site establishment, whereas resistance to M. incognita appears quantitative, as evidenced by delayed nematode development and reduced reproduction in resistant genotypes.